Re: Minimum required of a system called "Namespaces in XML"

> yep
(more yeps then I expected;-)


> Besides, domain-names violate the persistence requirement. But yes,
> you want decentralized assignment...

That isn't actually a requirement, just an aside pointing out good
practice: that if you are using namespaces to get globally unique and
persistent names, then you should use globally unique and persistent
namespace name as a start. In fact most people seem to end up using
http URIs as namespace names which as you say are not particularly
persistent (cool uris don't change not withstanding). However no
namespace processor is expected to know every uri scheme and its
persistence properties, as it only uses the name as a string anyway
so there is no way you can make this a requirement.
http namespaces are clearly "persistent enough" for most purposes.

> Agreed with all of this. The issue with those of us who want to 
> build something on top of this is that the XML namespace 'name'
> shouldn't prevent someone from attempting to resolve it. Allowing
> a relative URI without a BASE is an error and thus makes it so that
> the namespace 'name' prevents someone from attempting to resolve it.

It is not clear that there is anything you can not do with xmlns="foo"
that you could do with xmlns="mailto:michaelm@netsol.com"
you can't use either to dereference any information and while you could
use the latter in an rdf assertion that would be an assertion about
your mailbox, not about any namespace. If you really want to always
have an absolute URI from every namespace name just take some fixed
base as has been discussed before.

There is absolutely no point in trying to dereference an arbitrary
namespace name as typically you will just get a missing file error,
so anyone specifying some system that does do this is going to have to
say which namespace names their system works with. relative URI
will either have to be specified to not work with the system, or the
system will have to cope with the fact that (as is normally the case
with relative URI) what you get if you dereference it depends on the
current base.

Note that the XML 1.0 rec was carefully written _not_ to assume that
a non validating processor had any access to any external entities.
Of course it needs access to the document entity, if nothing else,
about which it says

> This specification does not specify how the document entity is to be
> located by an XML processor;
> unlike other entities, the document entity has no name and might
> well appear on a processor input stream without any identification
> at all.

So it is explictly envisioned by the xml spec that the parser should
not know any URI for its input, and thus would find it impossible to
implement any newly enforced requirement to make relative URI
absolute.

Making relative URI as namespace names allowed, except where there
is no base URI is totally unacceptable it means that 
cat xml-file
(which just displays the contents on standard out) could potentially
turn a valid document into a non conforming one.

Your statement would imply that the only thing discussed on this list
is banning (or changing the meaning of) namespaces with names being a
relative URI. That was the original topic of the list but my message
was essentially triggered by the alarm at repeated suggestions from
various quarters of changing the semantics of _all_ documents using
namespaces, so that for example http://www.w3.org/1999/XSL/Transform
and http://WWW.w3.org/1999/XSL/Transform should be "equivalent"
namespaces or the latter should be an error, or that any URI
at all which, when dereferenced, produced the same HTML file as the
above should also name the "same" namespace.

Even if you ban relative URI as namespace names then you have to be
able to answer the following question.

Take an rdf assertion about some existing resource identified by
an absolute URI, where this resource is unconnected with namespaces.

Now consider the document

<xxx xmlns=" . . . that URI . . ." />

Questions

1) Is this a well formed XML document conforming to the XML namespace
   recommendation.

answer: yes

2) What is the name of the namespace of the element contained in the
   document 

answer: " . . . that URI . . ."

3) Is it possible to make an rdf assertion about the namespace used in
   this document.

answer: I don't know. But if it is it had better use a different URI
to the rdf assertion that you started with.

The only really substantive objection that has been made against
relative URI as namespace names is the fact that you can not use them
with rdf, but until I can understand this last question (ie until
I can understand how you can use even absolute uri for this purpose)
I can not really get any feeling for whether or not this is a real
problem.

David

Received on Monday, 5 June 2000 13:16:12 UTC